Abstract: The enzyme-induced calcium carbonate precipitation (EICP) technique strengthens soil and reduces permeability by cementing soil particles with calcium carbonate. However, limited penetration of solutions between soil particles hinders cementation in saturated environments, necessitating systematic investigation of EICP reinforcement in underwater, unconsolidated sandy layers, such as seabed and lakebeds. In this study, we developed a model test system for underwater EICP grouting and implemented controlled pore-water flow in underwater sandy layers using a perfusion–drainage liquid cycle. During EICP reinforcement, we measured the conductivity, pH, and Ca²⁺ concentration of the reaction solution in embedded and drainage pipes to characterize changes in mineralization efficiency in saturated sand. Additionally, by tracking the model’s overall permeability as a function of reinforcement cycles and applying electrical-resistance tomography, we systematically characterize reinforcement effects and the spatiotemporal evolution of grout diffusion in underwater sands. 1) The perfusion–drainage system enables EICP grouting reinforcement in water-rich sandy layers. The saturated-sand permeability decreases from 1.28×10⁻² m/s to 9.66×10⁻⁵ m/s after 10 EICP treatments. 2) The slurry diffuses from both sides of the grouting pipe toward the center pumping pipe, with high conductivity, low pH, and Ca²⁺ enrichment, indicating continued diffusion and mineralization as resistivity declines toward stabilization and pore space becomes filled. 3) Resistivity varies significantly with depth and location, indicating uneven reinforcement in large-scale soil masses. These findings provide a theoretical basis for applying EICP technology to seabed foundation reinforcement and submarine landslide mitigation.

Key words: enzyme-induced calcium carbonate precipitation (EICP), model test, underwater grouting, electrical resistance tomography, anti-seepage and reinforcement